Busy signal for telephone-exchanges.



No. 777,801. PATENTED DEC. 13, 1904. J. L. MOQUARRIE. BUSY SIGNAL FORTELEPHONE EXCHANGES.

APPLICATION FILED APR. 1, 1901.

.NO MODEL. 2 SHEETS-SHEET 1.

PATENTED DEC. 13, 1904.

J. L. MGQUAEEIE.

' BUSY SIGNAL FOR TELEPHONE EXCHANGES.

APPLICATION FILED APR 1 1901.

2 SHEETS SHEET 2.

N0 MODEL.

UNITED STATES Patented December 13, 1904.

PATENT OEEicE.

ELECTRIC COMPANY, OF CHICAGO,

ILLINOIS.

ILLINOIS, A CORPORATION OF BUSY SIGNAL FOR TELEPHONE-EXCHANGES.

SIEGIFICAIION forming part of Letters Patent No. 777,301, dated December13, 1904. Application filed April 1, 1901. Serial No. 53,874. (Nomodel.)

1'0 aZZ who/1 it may concern/.-

Be it known that I, JAMns L. McQUAnarE, a citizen of the United States,residing at Chicago, in the county of Cook and State of 5 Illinois, haveinvented a certain new and useful Improvement in Busy Signals forTelephone-Exchanges, of which the following is a full, clear, concise,and exact description.

My invention relates to a busy signal for I telephone-exchanges, and hasfor its object to relieve the central-oilice operator from the duty oftesting each called line to find out if it is free before makingconnection therewith. At present in all large exchanges each line isprovided with a number of multiple springjacks, oneon each section ofthe switchboard, and it is necessary that each operator before makingconnection with any line at her section of the board should first make atest to ascertain whether or not a connection has already been made withthe line at a springjack of some other section. Then if the line isengaged the operator must notify the calling subscriber of that fact andthat he must 2 5 wait until the line called for is disengaged before hecan have the desired connection. The usual busy-test system comprisesmeans brought into action by connection with any spring-jack of alinefor establishing a pecul- 3 iar electrical condition at all the otherspringjacks of that line, which condition may be perceived by anoperator at any section upon touching the tip of her connecting-plugwith a contact-terminal or test-ring of the jack 3 5 and listening inher telephone-receiver. This test by the operator occupies aconsiderable portion of the time required to complete a connection fromone line to another, and it is evident that if it could be eliminatedthe bur 4 den upon the operator would be greatly lessened and theefiiciency of telephone service materially increased.

I have devised a system wherein the operator may immediately makeconnection with the line called for without testing, and if the line isalready engaged a signal will automaticallybe transmitted to the callingsubscriber which will apprise him of the fact. If the called line isbusy, the mere act of making connection with another spring-jack of theRO line will not complete the circuit; neither will ringing-current beapplied to that line, but instead a peculiar signal wouldautomaticallybe transmitted over the calling-line, which will be perceived by thecalling party and understood by him to mean that the called line isbusy. This signal maybe produced by inducing in the circuit of thecalling-line a rapidly-varying current, which will cause a hum or tonein the subscribers telephone, or a phonograph may be used to transmitspoken words, or any other desired signal may be employed.

My invention consists in certain combinations of apparatus and circuitshereinafter to 5 be described, and particularly defined in the appendedclaims.

The accompanying drawings illustrate diagrammatically atelephone-exchange system embodying my invention, and I will proceed 7to describe said invention particularly by reference to the drawings.

Figure 1 is a diagram showing two subscribers telephone-lines extendingfrom substations to multiple springjacks at a central office and anoperators pair of plugs and plugcircuit for uniting the lines. Thesystem is equipped and arranged in accordance with my invention. Fig. 2is a skeleton diagram illustrating the condition of the apparatus andthe path of the ringing-current when a callingdug is inserted. in thejack of a free line, and Fig 3 is a similar diagram showing thecondition of the apparatus when the operators calling-plug is insertedin a jack of a line 8 5 already connected at another section of theswitchboard. This figure shows how the busysignal current is applied tothe calling line.

Similar letters and figures of reference are use to designate the sameparts wherever 9 shown.

The subscribers apparatus at each of the substations A B is of the usualtype, comprising a transmitting and a receiving telephone, aninduction-coil, a condenser, and a signalbell, all associated togetherin a well-known manner, and having a switch-hook for the telephone toout the talking apparatus out of circuit when not in use. Thesignal-bell is included with the condenser in a bridge of the Y Eachtelephone-line extends in two limbs 1 2 to the central-ofiiceswitchboard and is provided with multiple spring-jack terminals 0 a atthe several sections of the board. A battery b is normally connectedwith a line-relay 0 in a bridge of the line by way of the armatures andback contacts of a cut-off relay (Z. The line-relay 0 controls asubsidiary signallamp 0. The magnet of the cut-ofi relay is ofcomparatively high resistance, and an extra back contact (Z' is providedfor one of its armatures, said contact being connected with anintermediate point in the winding. Normally, then, a portion of themagnet-winding of the cut-off relay is short-circuited at con tact d;but when the magnet draws up its armature the contact is broken and theresistance of the whole winding introduced into the circuit. The cut-offrelay of each line is included in the circuit of a conductor 3, whichextends from ground to all the test-rings a a of the spring-jacks ofthat line.

The operator at the central ofiice G is provided with a number of pairsof plugs e f for connecting any two lines together by plugging into thespring-jacks of the lines. Each plug has three contact-pieces adapted toregister with the two contact-springs and the test-ring, respectively,of any spring-jack into which it may be inserted. Thus plug a, which isthe answering-plug, has tip, ring, and sleeve contacts e 6 2 andsimilarly plug f, which is the calling or connecting plug, hascorresponding tip, ring, and sleeve contacts f f f. The tip and ringcontacts of each plug are connected, respectively, with the tip and ringcontacts of its mate by the link conductors i 5 of the plug-circuit, anda battery g is connected in a bridge of said conductors 4 5 between thewindings of a repeating-coil in the usual manner. The pole g of saidbattery is grounded. The answering-plug has the usual cord-circuitconnections. A supervisory relay e in the ring-strand 5 controls a shuntabout the supervisory signal-lamp 6 which is connected in a conductor 6,leading from the pole g of the central battery to the sleevecontact 0 ofthe plug. The conductor 6 also includes the magnet-winding of a relay h,which is adapted when excited to close a branch circuit 7 from thebattery g to ground through a resistance 6 and supervisory signallamp71:.

Four relays Z on a 0 are associated with the calling-plug f forcontrolling the automatic ringing and busy-signal circuits. The relay Zis in the nature of a supervisory relay and is included in thering-strand 5 of the callingplug. The relay m controls the continuity ofthe cord-circuit and is in the nature of a ringing-key. It has twowindings m m of which the former is included in a branch conductor 8,leading to ground by way of the armature and front contact of relay Z inshunt of the supervisory lamp in. The other winding, m is included in ashunt-path about the resistance 2', said shunt being made up ofconductors 9 8 and being controlled by one of the armatures, m and itsfront contact of relay m. The relay Z being included in one of the mainconductors 5 of the plug-circuit is responsive to the flow of current inthe line with which plug f may be connected. WVhen said relay Z isexcited, it closes the ground branch 8 through the winding m, shuntingout the lamp 7c and exciting relay m. The latter relay then closes thecircuit 8 9 through its sticking-winding m and thereupon becomesindependent of relay Z. The relay m has two armatures m of, whichcontrol the continuity of link conductors L 5, respectively, of theplug-circuit. Said link conductors are normally broken, and the endsthereof which lead to the calling-plug are adapted to be connected bythe switch-contacts of the other relays 0 and n with ground and with thegrounded generator p, respectively, in a manner presently to bedescribed. The relays 0 and 12 are both included in parallel paths of aconductor 10, leading from a connection with pole g of battery 9 to thesleeve-contact f of the calling-plug. The relay n has two armatures a M,of which the former is connected with the front contact of relay 0,whose single armature is connected with the grounded generator 1) by aconductor 11. The front contact of armature n is connected to the backcontact of armature m so that relay m being inert and relays n and 0excited calling current from said generator will find its way to thering contact of the calling-plug.

The armature n of the relay a is connected to the conductor 10 and itsfront contact is connected by a conductor 12 with the back contact ofarmature m". Relay m being inert then and relays n and 0 excited,ringingcurrent from generator p sent out from the ring contact of thecalling-plug to limb 2 of the telephone-line after passing through thebridge at the substation will find a return-path over limb 1 of the lineto the tip of the plug and conductor 4:, to armature m conductor 12,armature n conductor 10, to ground through the battery g. The backcontact of armature n is connected with an intermediate point of thewinding of relay a, so that normally a part of the winding isshortcircuited.

The relays a and 0 are both excited whenever the calling-plug f isinserted in the spring-jack of a free line, current for exciting saidrelays passing from grounded battery g through conductor 10 to thesleeve f of the plug and thence to the ground by way of the test-ring ofthe jack and conductor 3 connected therewith, said conductor includingthe winding of the cut-off relay all; but while relay 0 is extremelysensitive and always draws up its armature whenever the plug f isinserted in the jack of any line, whether free or not, the other relay,12/, is not so sensitive and a part of its winding is normallyshortcircircuited. If then the plug f be inserted in the jack of a linewhich already has a conneetion at another jack, the diflerence ofpotential at the relay a will not be high enough to cause the flow ofsuflicient current to excite said relay-that is to say, therelay-circuit of the plug already connected with conductor 3, leading toground through the cut-oi]? relay, shunts the relay-circuit of any plugafterward inserted in any jack of the line, so that the relay a of suchlast-mentioned plug is not excited. It will be remembered, too, thatwhenever a plug is inserted in any jack of a line the drawing up of thearmatures of the cut-off relayof that line increases to a large extentthe resistance of the conductor 3 by removing the short circuit about aportion of the cut-off-relay windings. Again, the relay w of eachplug-circuit normally has a portion of its winding short-circuited,which makes it less sensitive, and when it is once excited sufficientlyto draw up its armatures the short circuit is broken and the wholewinding included in the circuit.

The back contact of armature n is connected with the conductor 5 of theplug-circuit, from which a path to ground can be traced through thebattery g and a winding of the repeatingcoil. Therefore if relay 0should be excited and relay it remain inert current from theringing-generatorp will find a path through said winding of therepeating-coil by way of conductors 11 and 5. This current passingthrough one winding of the repeating-coil will induce currents in theother windings, which find circuit through the line of the callingsubscriber. I have shown a secondary winding of an induction-coil 9included in the conductor 11, and the primary of said induction-coil isincluded in a local circuit with a source of current a and aninterrupter a. By this means an alternating current of high frequencymay be superimposed upon the ringing-current from the generator 1). Thishighfrequency current being transferred by induction througl'i therepeating-coil to the line of the calling subscriber will cause a hum ortone to be produced in his receiver, which he will recognize as a busysignal. Instead of the tone test it is evident that a phonograph orother signal device might be employed to'send out the busy signal.

The operator is provided with the usual telephone set and is providedwith a key for connecting the same in bridge of the cord-circuit,whereby she may communicate with subscribers.

till;

The operation of the system may be reviewed as follows: Assume thatsubscriber A desires to communicate with subscriber B. The removal ofhis telephone from its switchhook closes a bridge of the line, wherebycurrent from the battery Z) finds circuit through. the line-relay,excites the same, and causes the illumination of the line signal-lamp c.The operator at that section of the multiple switchboard at whichsubscriber As lalinp is located perceiving the signal inserts heranswering-plug into the spring-jack oi As line at her section of theboard and upon listening in inquires the number of the line wanted.Having ascertained that the line to substation B is wanted, theoperator, without making any test to ascertain whether or not Bs line isbusy, inserts the other or calling plug of the pair into the spring-jackof Bs line, thus completing the connection. l f l s line is not alreadyengaged, the insertion of the callingplug ih his spring-jack will 'auseringing-current to be automatically applied to his line. The conditionof the operatorsplug-circuit apparatus at this stage is'shown in Fig. 2,and the path of the ringing-em'rent is illustrated by heavy lines. Bothrelays n and 0 have been excited by current in conductor 10, as shown,upon completion of the circuit by the insertion of the plug in the jackof the called line. Relays land m. are as yet inert, because theresistance of the bell-bridge at the substation is so great thatsuliicicnt current does not pass through relay Z to excite the same; butwhen the subscriber at the called station answers by removing histelephone from the switch-hook the closing of the low-resistance bridgeof the line through the talking apparatus causes an increase in thecurrent flowing through relay Z, whereby said relay becomes excited anddraws up its armature. Circuit is thus closed through winding m of relaym to ground, shunting out the signallamp, which was lighted when theanswering plug was first inserted. Relay m in drawing up its armaturescuts olf the ringing-current and establishes the complete circuit of thelink conductors 4r 5 from the calling to the answering plug, so thatsubscribers A and B are thus connected together for conversation. Thedrawing up of armature m closes the circuit through the sticking-windingin, so that relay in is now rendered independent of the switch at thecalled station and is maintained excited as long as the plugs remain inthe spring-jacks. The relay Z still acts as the supervisory relay of thecalled line and is maintained excited by current from battery as long assubscriber Bs telephone is oil its book. When the conversation isfinished and the subscribers hang up their telephones, the shunts aboutsupervisory lamps and Z: are broken by the deenergization of relays cand 6, respectively, whereby said lamps become illummated to indicate asignal for disconnection.

In disconnecting the operator will first remove the calling-plug f andthen the answering-plug e to avoid sending a false ringing-signal overthe called line, which would otherwise result by reason of thedeenergization of the relay m; but assuming now that subscriber A hascalled for a connection with subscriber B, but subscriber Bs linealready has a connection at some other section of the multipleswitchboard, the full resistance of the cut-off relay (Z is thereforeincluded in the ground conductor 3 from the test-rings of the jacks ofthat line. The operator may plug in without making any test; but onlythe sensitive relay 0 will be excited, the path including relays n and 0being shunted by the circuit already established. The condition of theapparatus and circuits at this time is illustrated in Fig. 3, and thepath of the busy-tone current is shown in heavy lines. Relay 0 alonebeing excited, the current from generator 9, upon which is superimposedthe tone-producing current, finds path through one winding of therepeating-coil, and thus induces a similar current in the line to thecalling-station. The calling subscriber, listening in his telephone forthe response of the called party, hears instead the tone produced by theinduced current, and, recognizing this as a notification that the lineis busy, hangs up his telephone. His supervisory lamp is thus lighted,giving to the operator the signal for disconnection.

When a calling-plug of one cord-circuit has been connected With one ofthe jacks of a line and the line is afterward plugged into at anotherjack, it may be thought that the relay mechanism of the first plug wouldbe disturbed by the establishment of the second parallel circuit. Theanswer to this objection is that the relay n of the plug first insertedin drawing up its armature n has removed a short circuitabout a portionof its winding, so that the entire Winding receives current. The relaywill thus hold up its armature under considerably less current than isrequired to draw up the armature in the first place.

If connection should be made with a line busy at the moment, but fromwhich the first connection is removed While the second plug remainsinserted, it is desirable that the busy signal should be maintained uponthe second plug-circuit and that the substation of the telephone-lineshould not be rung the instant the first connection is removed, sincethe called subscriber would not be apt to recognize this as indicating adiiferent connection. This result is accomplished by means of theimproved construction of the cut-off relay, whereby a a connection withthe line causes said relay to break a short circuit normally maintainedabout a portion of its Winding, thus increasing the resistance of theconductor 3. This increase in resistance causes the potential to drop,so that the relay n of the last plug inserted will not respond, eventhough the plug first inserted should be removed.

Since in an average city exchange only about ten per cent. of the callshave to be abandoned because the line of the called party is busy, it isevident that the elimination of the operators busy test from the otherninety per cent. efiects a clear saving of a great amount of time, theburden on the operator being decreased and the efliciency of thetelephone service correspondingly increased.

It is evident that many modifications may be made by those skilled inthe art Without departing from the spirit of my invention. I do not,therefore, Wish to be understood as limiting myself closely to theparticular apparatus and circuits, but claim broadly as my invention thefollowing:

1. The combination with a telephone-line having a number of multiplespring-jack terminals, of a calling-plug and a plug-circuit therefor, asource of signaling-current adapted to be connected With theplug-circuit, an electromagnetic relay device controlling theapplication of the aforesaid signaling-current to the plug-circuit, acircuit for said relay device adapted to be established in registeringcontacts of the plug and a spring-jack of the telephone-line, wherebythe operation of said relay device is aifected by the electricalcondition of the spring-jack into Which the callingplug is inserted,said relay device being sensitive to an abnormal electrical condition ofsuch spring-jack, other plugs for making connection with the line, andmeans, brought into action by connection with any spring-jack of thetelephone-line, for changing the electrical condition of the severalmultiple spring-jacks of that line, whereby said source ofsignalingcurrent is applied to the plug-circuit of the calling-plug uponits insertion into one springjack of the line when a connection alreadyexists at another spring-jack thereof, to transmit a busy signal oversaid plug-circuit, substantially as set forth.

2. The combination with a telephone-line having a number of multiplespring-jack terminals, of a calling-plug and a plug-circuit therefor, asource of calling-current adapted to be connected with the calling-plug,electromagnetic relay mechanism controlling the application'of saidcalling-current to the callingplug, a circuit for said relay mechanismadapted to be established in registering contacts of the plug and anyspring-jack of the telephoneline, said relay mechanism being sensitiveto the electrical condition of the spring-jack into which thecalling-plug is inserted, other plugs for making connection With theline, and means, brought into action by connection with any springjackof the telephone-line for changing the electrical condition of theseveral multiple spring-jacks of that line, and so for preventing thenormal operation of said relay mechanism when the calling-plug isinserted in a jack of the telephone-line while a connection exists atanother s1 )ring-jack of said line, substantially as set forth.

3. The combination with telephone-lines each having a number of multiplespring-jack terminals, of plugs and their plug-circuits for makingconnection with the telephone-lines, a local circuit including aresistance (Z, associated with each telephone-line, having parallelbranches, one in each plug-circuit, each of said parallel branches beingadapted to be closed in registering contacts of its plug and aspring-jack of the line, a magnet in each of said parallel branches, anda source of current in the circuit, said source of current and theseveral magnets being proportioned or adjusted to one another so thateach of said magnets is adapted to respond to the flow of current in itsbranch when that branch alone is closed, b utnot to respond when thecircuit of its branch is completed in shunt of a branch alreadyestablished at another spring- 'iack of the line, substantially setforth.

4:. The combination with telephone-lines each having a number ofmultiple spring-jack terminals, of plugs and their plug-circuits formaking connection with the telephone-lines, a local circuit including aresistance (Z, associated with each telephone line, having parallelbranches, one in each plug-circuit, each of said parallel branches beingadapted to be closed in registering contacts of its plug and aspring-jack of the line, a magnet in each of said parallel branches, asource of current in the circuit, said source of current and the severalmagnets being proportioned or adjusted to one another so that each ofsaid magnets is adapted to respond to the flow of current in its branchwhen that branch alone is closed, but not to respond when the circuit ofits branch is completed in shunt of a branch already established atanother spring-jack of the line, and switching mechanism, operated bysaid magnet, controlling the plug-circuit with which said magnet isassociated, substantially as set forth.

5. The combination withtelephone-lines each havinga number of multiplespring-jack terminals, of plugs and their plug-circuits for makingconnection with the telephone-lines, a local circuit including aresistance a, associated with each telephone line, having parallelbranches, one in each plug-circuit, each of said parallel branches beingadapted to be closed in registering contacts of its plug and aspringjack of the line, a magnet in each of said parallel branches, asource of current in the circuit, said source of current and the severalmagnets being proportioned or adjusted to one another so that each ofsaid magnets is adapted to respond to the flow of current in its branchwhen that branch alone is closed, but not to respond when the circuit ofits branch is completed in shunt of a branch already established atanother spring-jack of the line, a source of signaling-current, andswitching mechanism, operated by said magnet, controlling theapplication of said signaling-current to the plug-circuit, whereby abusy signal is transmitted. over the plug-circuit when connection ismade with a busy line, substantially as set forth.

6. The combination with two telephonelincs extending from substations toa central office, of a pair of plugs and link conductors uniting themfor connecting said telephonelines together in response to a call from asubstation of one of said lines, multiple springjack terminals for thecalled. line, a source of signaling-current, an instrument at thecalling-station responsive to such signaling-current, a third plugadapted to be connected with one of the spring-jacks of the called line,relay mechanism for applying said source of signaling-current to thecalling-line, and means, controlled jointly by the insertion of both thecallingplug of the pair uniting said two lines, and the third plug, intomultiple spring-jacks of the called line, for controlling said relaymechanism, substantially as set forth.

7. The combination with a called line having a number of multipleterminals, and a connectioirswitch temporarily applied to one of saidterminals, means controlled by said connection-switch for establishing apeculiar electrical condition to constitute a busy signal at the othermultiple terminals, a ca1ling-line and a connection-switch for unitingthe same with the called line at one of said terminals, amagnotassociated with the last-mentioned connection-switch sensitive to thebusy signal produced by the first mentioned connectionswitch, a sourceof signaling-currcnt and a switch for applying the same to thecallingline, controlled. by said magnet.

8. The combination with a telephone-line and multiple-terminalspring-jacks thereof and a calling-line terminating in a plug forconnection with one of said multiple jacks, a signal-receivinginstrument at the substation of said calling-line connected in theline-circuit, a source of busy-test current at the central ol'lice and alocal circuit formed in part of conductors terminating in the terminalplug of said calling-line and the spring jack or socket of the calledline, and in part adapted for completion through registeringcontacts ofanother spring-jack and the plug uniting a different line with saidspring-jack, whereby the user of the calling-line receives a busysignal,a switch at the substation of the calling-line and a clearing-out signalconnected with the line at the central oliice controlled by said switch,whereby the user of the telephone may call for disconnection afterreceiving the busy signal, as described.

9. The combination with a telephone-line having two or more terminalsand link con- IIO ductors at each or said terminals for makingconnections therewith from other lines, means adapted to change theelectrical condition of said line in making connection therewith by anyof said link conductors, an electromagnet in connection with one of saidlink conductors sensitive to the electrical condition of the line, and aswitch in the link conductor controlled through the agency of saidmagnet; whereby when the line is engaged by connection at one terminal,aconnection made at another terminal is inefiective, as described.

10. The combination with a telephone-line having multipleconnection-terminals and connection-switches with their respective linkconductors for making connection with the line at any terminal, meanscontrolled by applying a connection-switch to one terminal forestablishing a changed electrical condition at the other terminals, anelectromagnet n associated with one of said connection-switchessensitive to the electrical condition of the terminal to which saidconnection-switch is applied, a source of signaling-current adapted tobe applied to the link conductor associated with said last-mentionedconnection-switch, and switching mechanism governedby said magnetcontrolling a break in said link conductor and also controlling theapplication of said signaling-current, whereby an attempted J connectionwith a busy line is rendered ineffective and a warning signal given, asdescribed.

11. The combination with a telephone-line having two or more terminalsand link conductors at each of said terminals for making connectionstherewith from other lines, means adapted to change the electricalcondition of said line in making connection therewith by any of saidlink conductors, an electromagnet n in connection with one of said linkconductors sensitive to the electrical condition of the line, a switchoperated through the agency of said magnet, controlling a break in thecircuit of said link conductors, and a locking-winding for said magnet,the excltement of said locking-winding being dependent upon theconnection of the corresponding link conductor with the said line,substantially as described.

In witness whereof I hereunto subscribe my name this 20th day of August,A. D. 1900.

JAMES L. MOQUARRIE. l/Vitnesses:

, ELLA EDLER,

DUNCAN E. XVILLETT.

